1. Field of the Invention
This invention is related generally to safety valves. More particularly, this invention pertains to subsurface safety valves deployed in a wellbore for controlling fluid flow through a production tubing string. More particularly still, the present invention relates to a lockout tool for locking out a safety valve into its open position.
2. Description of the Related Art
Subsurface Safety Valves (SSVs) are often deployed in hydrocarbon producing wells to shut off production of well fluids in emergency situations. Such SSVs are typically fitted into production tubing in the wellbore, and operate to block the flow of formation fluids upwardly through the production tubing should a failure or hazardous condition occur at the well surface.
SSVs are designed either to be slickline retrievable, or tubing retrievable. If a safety valve is configured to be slickline/wireline retrievable (WRSSV), it can be easily removed and repaired. If the SSV forms a portion of the well tubing, it is commonly known as “tubing retrievable” (TRSSV). In this instance, the production tubing string must be removed from the well to perform any safety valve repairs.
The subsurface safety valve has a flapper member or “plate,” that is moveable between an open position and a closed position. In this respect, the flapper member is typically pivotally mounted to mate with a hard seat. When the flapper is in its open position, it is held in a position where it pivots away from the hard seat, thereby opening the bore of the production tubing. However, the flapper is biased to its closed position against the seat.
The flapper of the safety valve is held open during normal production operations. This is done by the application of hydraulic fluid pressure transmitted to an actuating mechanism. A common actuating mechanism is a cylindrical flow tube, which is maintained in a position adjacent the flapper by hydraulic pressure supplied through a control line. The control line resides within the annulus between the production tubing and the well casing. Pressurized hydraulic fluid is delivered from the surface through the control line, and bears against a piston. The piston, in turn, acts against the cylindrical flow tube, which in turn moves across the flapper valve to hold the valve open. When a catastrophic event occurs at the surface, hydraulic pressure is interrupted, causing the cylindrical flow tube to retract, and allowing the safety valve to quickly close. When the safety valve closes, it blocks the flow of production fluids up the tubing. Thus, the SSV provides automatic shutoff of production flow in response to well safety, conditions that can be sensed and/or indicated at the surface. Examples of such conditions include a fire on an offshore platform, sabotage to the well at the earth surface, a high/low flow line pressure condition, a high/low flow line temperature condition, and operator override.
Removal and repair of the tubing retrievable safety valve is costly and time consuming. It is usually advantageous to delay the repair of the TRSSV yet still provide the essential task of providing well safety for operations personnel while producing from the well. To accomplish these objectives; the safety valve is disabled in the open position, or “locked out”. This means that the flapper member is pivoted and permanently held in the fully opened position. In normal circumstances, if the well is to be left in production, a WRSSV may be inserted in the well, often in lockable engagement inside a bore within the locked out tubing retrievable safety valve. Because of the insertion relationship, the WRSSV necessarily has a smaller inside diameter than the TRSSV, thereby reducing the potential hydrocarbon production rate from the well. Locking out the safety valve will not eliminate a need for remediation later, but the lockout and use of the WRSSV will allow the well to stay on production (most often, with a reduced production rate) or perform other work functions in the tubing until the TRSSV can be repaired or replaced.
Various types of mechanical lockouts have been proposed. Examples are found in U.S. Pat. Nos. 3,696,868; 3,786,865; and 3,786,866. In these applications, various additional parts are necessary to enable the valve to be locked out. Such parts are integral to each and every valve. It is interesting to note that modern SSVs are extraordinarily reliable, and such lockout mechanisms are not used except in a small fraction of the total valve population; yet, integral lockout mechanisms are present in, and add unnecessary cost to, most prior art SSV assemblies. Further, integral lockout mechanisms are not normally operated for extended periods of time, often for years, and are not normally or even periodically actuated. For these reasons, the integral lockout mechanisms may themselves fail to work for various reasons such as sand, corrosion, scale and asphaltine buildup.
Other inventors have realized the disadvantages of integral lockout mechanisms, and inventions have been disclosed in U.S. Pat. No. 4,574,889 (Pringle '889), U.S. Pat. No. 4, 577,694 (Brakage, Jr. '694) and U.S. Pat. No. 6,059,041 (Scott '041). These inventions recognize a need to remove integral lockout mechanisms and requisite structure from the SSV.
Pringle '889 teaches a method and apparatus of locking out a subsurface safety valve. The apparatus provides a housing having a bore and one downwardly directed shoulder adjacent the bore. The shoulder makes an outward indentation in the flow tube at a predetermined location whereby the indentation will engage a downwardly directed shoulder in the housing, preventing the flow tube from moving to the closed position. The mechanism has the limitation of making only a single indentation during any stroke of the lockout tool. This results in very high localized stresses at the point of impact, causing embrittlement of the material, and possibly undesirably punching through the flow tube. Further, there is no mechanism disclosed to index the punching mechanism to another radial position. Because the SSV assembly is often placed thousands of feet below the earth's surface, using the device taught by Pringle '889 to make second or subsequent indentations in the flow tube in any other radial position is unreliable. Therefore, the operator can only be assured of making a single indentation or, worse, a single penetration of the flow tube. When penetration occurs a metal flap is formed, usually connected by a very small area of metal resembling the infamous “hanging chad” of Florida election lore. A SSV that is locked out in such a manner may not stay locked out when slickline, coiled tubing or other remediation procedures are performed on the well below the SSV. In this respect, when such service tools are pulled up through the locked out SSV, shearing the indentation or flap can occur, resulting in an undesirable unlocking of the valve. Such unlocking can lead to the well again being prematurely shut in, and a resultant loss of production.
Brakage, Jr. '694 teaches a method and apparatus for permanently locking a shiftable valve member in a well conduit in an open position. The invention provides a spring metal band that is adapted to expand from a contracted, run-in position to a radially enlarged locking position. The band thereby holds the valve member in an open position. The band is deposited in the SSV by a specially adapted slickline tool. While this invention satisfies the need to remove the integral lockout from the safety valve, an additional part, (the spring metal band) is introduced into the SSV assembly downhole. Further, after deposition, the metal band is not positively attached to anything inside the SSV, but is held in place only by the frictional force exerted by the spring metal band. Certain flow regimes in the wellbore can collapse the spring metal band and allow it to flow out of the SSV, thereby causing the well to inadvertently shut in. This phenomenon has been observed.
Scott'041 is similar to Brakage Jr. '694 wherein deposition of a radially deflectable blocking member relative to the SSV is provided to enable lockout. In a described embodiment of the apparatus, a lockout tool has mechanisms which effect latching of the tool to an internal profile of a safety valve, displacement of a flow tube of the safety valve to open the safety valve, and deposition of an expandable ring to prevent closure of the safety valve. This invention only partially satisfies the need to remove the integral lockout from the safety valve, because it requires expensive special profiles and again introduces an additional part to enable the lockout. While this is an arguable design improvement over Brakage Jr. '694, certain flow regimes still may flow the radially deflectable blocking member out of the SSV, thereby causing the well to inadvertently shut in.
There is a need, therefore, for a lockout tool that requires no additional integral SSV parts or expensive special profiles to enable lockout of an SSV. Further, there is a need for a lockout tool that can be deployed by slickline or coiled tubing, and does not attempt to permanently deposit any parts in the safety valve to enable lockout. Still further, there is a need for a lockout tool that does not require special profiles or shoulders in the valve, and can be used to lock out virtually any type of safety valve made by any manufacturer.